How to get the number of comments on a post - angularjs

Question

I'm trying to get the number of comments a post has, but can't find a way to do it. I have a plunk if you want to check it.
<div class="anuncios">
<div class="panel panel-default" ng-repeat="posts in post | orderBy:'-FechaAnuncio'">
<div class="panel-heading" style="overflow:hidden;">
<p>{{posts.NombreLocal}}</p>
</div>
<div class="panel-body">
<p>{{posts.Anuncio}}</p>
<hr>
<small>{{posts.FechaAnuncio | date:'HH:mm:ss dd-MM-yyyy'}}</small>
<button class="btn btn-primary" style="float:right;" ng-click="showme = !showme"><span ng-hide="showme">Show Comments: {{posts.comments.length}}</span><span ng-show="showme">Hide Comments</span></button>
<div>
<div class="well" ng-show="showme">
<div class="input-group">
<input type="text" class="form-control" placeholder="Comment Here..." ng-model="comment.text">
<span class="input-group-btn">
<button class="btn btn-default" type="button" ng-click="addComment(posts, comment)">Publish!</button>
</span>
</div>
<!-- /input-group -->
<div class="cmt">
<div class="panel" ng-repeat="comments in posts.comments">
<p>{{comments.NombreLocal}}</p>
<p>{{comments.FechaComentario | date:'HH:mm:ss dd-MM-yyyy'}}</p>
<hr>
<p>{{comments.Comment}}</p>
<p></p>
</div>
<!--FIN DE COMENTARIOS -->
</div>
</div>
</div>
</div>
</div>
</div>
http://plnkr.co/edit/AIx0x7?p=preview
The number of comments should display next to "Show Comments:"
This is my Firebase Structure:
Firebase structure image

Answer 1

Since comments is an object, the easiest thing to do is to count the number of keys it has. You'll need to add this to your controller, or you could create your own filter.
app.controller('AnunciosCtrl', function($scope, $firebaseArray, $timeout) {
...
$scope.sizeOf = function(obj) {
return Object.keys(obj || {}).length;
};
});
HTML:
<span ng-hide="showme">Show Comments: {{ sizeOf(posts.comments) }}</span>
Plunker

Answer 2

In your controller do:
$scope.numComments = $scope.post.comments.length;
In your html :
...>Show Comments: {{numComments}}<...